As an oxygen concentrator of this type, as disclosed in Patent Literature 1 for example, a configuration of a PSA (Pressure Swing Adsorption) system using an absorbing material (zeolite) having properties such as selectively adsorbing nitrogen under increased pressure and discharging the adsorbed nitrogen under reduced pressure is known, and this system is also referred to as an adsorption system.
The oxygen concentrator having the adsorption system as described above is, as illustrated in FIG. 9 includes two sieve beds Ta, Tb filled with the absorbing material (zeolite) configured to adsorb nitrogen, a compressor C configured to supply compressed air to these sieve beds Ta, Tb, respective branch flow channels Fa, Fb configured to constitute part of air supply flow channel for supplying the compressed air from the compressor C to the two sieve beds Ta, Tb, respective air supply valves PVa, PVb configured to open and close the branch flow channels Fa, Fb independently, respective air exhaust flow channels Ea, Eb configured to open the respective sieve beds Ta, Tb to the atmosphere, and respective exhaust valves EVa, EVb configured to open and close the exhaust flow channels Ea, Eb independently.
The air supply valve PVa of the branch flow channel Fa continuing to one Ta of the two sieve beds is opened and the exhaust valve EVa of the exhaust flow channel Ea is closed, and simultaneously, the air supply valve PVb of the branch flow channel Fb continuing to the other Tb is closed and the exhaust valve EVb of the exhaust flow channel Eb is opened, so that oxygen at a high concentration can be obtained by supplying the compressed air to the one sieve bed Ta. In the meantime, since the other sieve bed Tb is decompressed, and hence nitrogen adsorbed to the zeolite is separated and discharged to the atmosphere. In addition, the air supply valves PVa, PVb and the exhaust valves EVa, EVb are switched into an inverted opening-and-closing pattern, so that oxygen at a high concentration can be obtained by supplying the compressed air to the other sieve bed Tb and, in the meantime, nitrogen adsorbed to zeolite of the one sieve bed Ta is separated and discharged to the atmosphere.
In other words, by switching the opening-and-closing pattern of the respective air supply valves PVa, PVb and the exhaust valves EVa, EVb alternately, the oxygen at a high concentration can be continuously obtained through the respective sieve beds Ta, Tb.
Now, as the air supply valves PVa, PVb and the exhaust valves EVa, EVb, a configuration in which a normally open electromagnetic pilot valve 20 is assembled to a diaphragm valve 10 as illustrated in FIG. 2, for example, is conceivable. In such a case, when the electromagnetic pilot valve 20 is OFF, pilot air is supplied to the diaphragm valve 10 via a pilot flow channel Fp branched from the air supply flow channel and the branch flow channels Fa, Fb and the exhaust flow channels Ea, Eb are closed and, in contrast, when the electromagnetic pilot valve 20 is ON, supply of pilot air to the diaphragm valve 10 is blocked and, in contrast, the branch flow channels Fa, Fb and the exhaust flow channels Ea, Eb are opened.
In this manner, in the case where the pilot flow channel Fp configured to supply the pilot air to the electromagnetic pilot valve 20 is branched from the air supply flow channel, immediately after the opening-and-closing pattern of the respective air supply valves PVa, PVb and the exhaust valves EVa, EVb is switched and the sieve bed configured to generate oxygen is switched from the one Ta to the other Tb, the other sieve bed Tb is in a state in which the pressure is still low due to the decompression until a moment immediately before, the pressure of the compressed air supplied from the compressor C drops temporarily as illustrated in FIG. 10, and simultaneously, the pilot pressure also drops.
On the other hand, the air supply valve PVa of the one sieve bed Ta, which is on the exhaust side, is to be supplied with pilot air and closed normally. However, since the residual pressure in the sieve bed Ta is still in a high state, the diaphragm valve 10 of the air supply valve PVa is opened because the pressures applied to both surfaces of a diaphragm 13 thereof are off-balanced (see hatched portion in FIG. 10) by dropping of the pilot pressure as described above and, consequently, exhaust air containing nitrogen at a high concentration flows temporarily reversely through the air supply flow channel and flows disadvantageously into the other sieve bed Tb, which is on the side where oxygen is generated.
The problem as described above occurs also immediately after switching of the sieve bed configured to generate oxygen from the other Tb to one Ta (see dot portion in FIG. 10).
In FIG. 10, vertical dot lines indicate timing of turning ON and OFF alternately of a distribution of power to the electromagnetic pilot valves 20 of the respective air supply valves PVa, PVb, that is, timing of switching of the opening-and-closing pattern of the respective air supply valves PVa, PVb and the respective exhaust valves EVa, EVb.
A temporary reverse flow of an exhaust air immediately after switching of the sieve beds Ta, Tb configured to supply the compressed air as described above may be caused not only by a drop of an air supply pressure of the air supply flow channel as described above, but also by other causes such as layout of the pilot flow channel.